EP0371343B1 - Titanium dioxide, process for its preparation and use thereof - Google Patents

Titanium dioxide, process for its preparation and use thereof Download PDF

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Publication number
EP0371343B1
EP0371343B1 EP89121252A EP89121252A EP0371343B1 EP 0371343 B1 EP0371343 B1 EP 0371343B1 EP 89121252 A EP89121252 A EP 89121252A EP 89121252 A EP89121252 A EP 89121252A EP 0371343 B1 EP0371343 B1 EP 0371343B1
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EP
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Prior art keywords
titanium dioxide
weight
hydrate
tio2
calcination
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German (de)
French (fr)
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EP0371343A1 (en
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Rene Dr. De Cleyn
Peter Dr. Thometzek
Jakob Dr. Rademachers
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Bayer AG
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Bayer AG
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Classifications

    • C—CHEMISTRY; METALLURGY
    • C03—GLASS; MINERAL OR SLAG WOOL
    • C03C—CHEMICAL COMPOSITION OF GLASSES, GLAZES OR VITREOUS ENAMELS; SURFACE TREATMENT OF GLASS; SURFACE TREATMENT OF FIBRES OR FILAMENTS MADE FROM GLASS, MINERALS OR SLAGS; JOINING GLASS TO GLASS OR OTHER MATERIALS
    • C03C1/00—Ingredients generally applicable to manufacture of glasses, glazes, or vitreous enamels
    • C03C1/04—Opacifiers, e.g. fluorides or phosphates; Pigments
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01G—COMPOUNDS CONTAINING METALS NOT COVERED BY SUBCLASSES C01D OR C01F
    • C01G23/00—Compounds of titanium
    • C01G23/04—Oxides; Hydroxides
    • C01G23/047—Titanium dioxide
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01G—COMPOUNDS CONTAINING METALS NOT COVERED BY SUBCLASSES C01D OR C01F
    • C01G23/00—Compounds of titanium
    • C01G23/04—Oxides; Hydroxides
    • C01G23/047—Titanium dioxide
    • C01G23/08—Drying; Calcining ; After treatment of titanium oxide
    • C—CHEMISTRY; METALLURGY
    • C03—GLASS; MINERAL OR SLAG WOOL
    • C03C—CHEMICAL COMPOSITION OF GLASSES, GLAZES OR VITREOUS ENAMELS; SURFACE TREATMENT OF GLASS; SURFACE TREATMENT OF FIBRES OR FILAMENTS MADE FROM GLASS, MINERALS OR SLAGS; JOINING GLASS TO GLASS OR OTHER MATERIALS
    • C03C8/00—Enamels; Glazes; Fusion seal compositions being frit compositions having non-frit additions
    • C03C8/14—Glass frit mixtures having non-frit additions, e.g. opacifiers, colorants, mill-additions
    • C03C8/20—Glass frit mixtures having non-frit additions, e.g. opacifiers, colorants, mill-additions containing titanium compounds; containing zirconium compounds
    • C—CHEMISTRY; METALLURGY
    • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
    • C09C—TREATMENT OF INORGANIC MATERIALS, OTHER THAN FIBROUS FILLERS, TO ENHANCE THEIR PIGMENTING OR FILLING PROPERTIES ; PREPARATION OF CARBON BLACK  ; PREPARATION OF INORGANIC MATERIALS WHICH ARE NO SINGLE CHEMICAL COMPOUNDS AND WHICH ARE MAINLY USED AS PIGMENTS OR FILLERS
    • C09C1/00—Treatment of specific inorganic materials other than fibrous fillers; Preparation of carbon black
    • C09C1/36—Compounds of titanium
    • C09C1/3607—Titanium dioxide
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2004/00—Particle morphology
    • C01P2004/30—Particle morphology extending in three dimensions
    • C01P2004/32—Spheres
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2004/00—Particle morphology
    • C01P2004/50—Agglomerated particles
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2004/00—Particle morphology
    • C01P2004/60—Particles characterised by their size
    • C01P2004/61—Micrometer sized, i.e. from 1-100 micrometer
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2004/00—Particle morphology
    • C01P2004/60—Particles characterised by their size
    • C01P2004/62—Submicrometer sized, i.e. from 0.1-1 micrometer
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2006/00—Physical properties of inorganic compounds
    • C01P2006/11—Powder tap density
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2006/00—Physical properties of inorganic compounds
    • C01P2006/12—Surface area
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2006/00—Physical properties of inorganic compounds
    • C01P2006/60—Optical properties, e.g. expressed in CIELAB-values
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2006/00—Physical properties of inorganic compounds
    • C01P2006/80—Compositional purity

Definitions

  • the present invention relates to titanium dioxide, a process for its preparation and its use in glass-like enamels and glazes as opacifiers.
  • Titanium dioxide is produced as a color pigment either by reacting TiCl4 with O2 or by hydrolysis of an aqueous solution of titanyl sulfate containing sulfuric acid and subsequent calcination.
  • the titanium dioxide hydrate suspension is calcined in a rotary tube furnace with residence times of 5 to 20 hours.
  • the precipitate resulting from the hydrolysis consists of fine particles with a specific BET surface area of 50-500 m2 / g, which undergo strong agglomeration during the calcination.
  • the agglomerates resulting from calcination form particles of 0.1 to 1.0 mm, which are composed of primary particles of 0.2 to 0.4 ⁇ m.
  • This material is not very suitable as a clinker or as a ground pigment for incorporation into glass-like enamels or enamels, since it clumps when mixed with the other constituents of the enamel frit in a dry state, which leads to an incomplete and inhomogeneous solution of the titanium dioxide during the The frit melts.
  • German Auslegeschrift 1 207 363 a process for the production of a TiO2 product for incorporation in glass-like enamels by calcining precipitated titanium dioxide hydrate is described.
  • the disadvantage of this method is that it is very expensive due to the two very different titanium dioxide hydrates that have to be prepared first.
  • TiO2 obtained in this way is that it is characterized by a high bulk density of 1.4 to 2 kg / l and has a low specific surface area of well below 1 m2 / g, which leads to low reactivity when melting in the frit .
  • US Pat. No. 2,721,787 describes free-flowing, non-dusting aggregates consisting of calcined anatase (primary particle size 0.2 to 0.3 ⁇ m, specific surface area 4.5 to 9 m 2 / g) and 0.1 to 3% of an inorganic binder .
  • These aggregates are produced by spray-drying aqueous slurries of hydro-classified titanium dioxide pigments, which originate from normal pigment production, at 150 to 400 ° C.
  • the disadvantage of this process is that calcined titanium dioxide pigments must first be prepared, which are then taken up in water to produce a slurry, in order to then spray-dry this slurry in order to obtain the claimed aggregates.
  • US Pat. No. 3,018,186 describes platelet-shaped titanium dioxide with a diameter of 1-20 ⁇ m and a thickness of 0.01-0.5 ⁇ m, which is almost exclusively in the rutile modification. These platelets are produced by calcining a titanyl sulfate solution containing at least 5% and at most 20% sulfuric acid in a flame at 800 ° C to 1800 ° C and residence times of 0.001-0.5 seconds. The material obtained is free of sulfuric acid and is used in ceramic and electrical materials, plastics and surface coatings as well as a filler. The titanyl sulfate solution used is complex to produce, since in pure form it is not an intermediate represents the pigment manufacturing process. The solution obtained by digestion of titanium ores contains considerable amounts of foreign elements such as Fe, Al, Mg and others
  • the task was therefore to provide a suitable titanium dioxide, which can be used as a clouding agent for glassy enamels and enamels.
  • the titanium dioxide according to the invention fulfills the above-mentioned requirements.
  • This titanium dioxide predominantly has isometric primary particles of the size from 0.5 to 5.0 ⁇ m, which are aggregated to predominantly spherulitic particles with diameters from 1 to 100 ⁇ m, and has a BET surface area of 1 to 4.5 m2 / g and a bulk density of 0.2 to 1.3 kg / l.
  • the BET surface area is determined according to DIN 66 131, Section 6, Oct. 1973 (5-point method, measuring gas: nitrogen, adsorption at the temperature of the boiling nitrogen, assumption of the area requirement of a nitrogen molecule of 0.162 nm2, pretreatment: 1 hour of heating in a stream of nitrogen at 130 ° C).
  • This titanium dioxide shows good stability, ie it does not break down into fine grains when mixed.
  • the hardness is not so great that, in combination with the primary particle size of 0.5 to 5 ⁇ m and the specific surface area of 1 to 4.5 m2 / g, the titanium dioxide has excellent digestion behavior Enamel melt results.
  • the 1 to 100 ⁇ m agglomerated particles are distributed evenly in the frit when mixed and then melt completely.
  • the digestion behavior is particularly favorable if the titanium dioxide according to the invention has a bulk density of 0.2 to 0.8 kg / l.
  • the particles form nearby areas rich in titanium dioxide, which act as germ cells for the recrystallization of titanium dioxide in the early stages of enamel firing.
  • the titanium dioxide according to the invention is present as rutile with more than 50% by weight and has a sulfate content below 0.5% by weight, preferably below 0.3% by weight, calculated as sulfate and based on titanium dioxide, and a titanium dioxide content above 90% by weight.
  • the titanium dioxide contains oxides, phosphates and / or silicates of the metals Li, Na and / or K in an amount of up to 0.5% by weight, based on titanium dioxide, and / or Mg, Ca, Sr, Ba, Sn, Sb, Bi, Y, Zr, Zn, V, Nb, W and / or Mo and / or oxides of the elements P and / or Si in an amount of up to 10% by weight, preferably up to 5% by weight, based on Titanium dioxide.
  • P2O5 improves the TiO2 recrystallization and thus the turbidity in the enamel.
  • the invention further relates to a suitable process for the preparation of the titanium dioxide according to the invention, wherein titanium dioxide hydrate with a BET surface area of 50 to 500 m2 / g is subjected to a short-term calcination with residence times of 0.1 to 60 seconds and at temperatures of 800 to 1600 ° C. .
  • the TiO2 hydrate can be introduced as an aqueous suspension into the calciner via a single or multi-component nozzle. However, it is also possible to feed the starting material to the calciner in the form of a pasty mass or as a dry powder. Short-term calciners come with conventional equipment such as Hot gas atomization reactors, reaction cyclones or flash calciners, which normally work with direct heating gas supply. However, indirect heating is also possible.
  • the product is separated outside the calcining chamber, for example using a cyclone or electrical or mechanical powder separator.
  • the calcination of the TiO2 hydrate is carried out between 1000 and 1300 ° C. with residence times of 0.1 to 5 seconds.
  • Titanium dioxide hydrate with up to 30% by weight sulfate, based on titanium dioxide or preferably precipitated sulfuric acid-containing titanium dioxide hydrate, is used as the starting material for the short-term calcination, as is e.g. arises in the pigment production process using the sulfate process.
  • auxiliary substances can be added to the titanium dioxide hydrate in a suitable manner before the calcination Form are mixed, which after calcination as oxides, phosphates and / or silicates of the elements Li, Na and / or K in an amount of up to 0.5 wt .-%, based on titanium dioxide and / or Mg, Ca, Sr , Ba, Sn, Sb, Bi, Y, Zi, Zn, V, Nb, W and / or Mo and / or as oxides of the elements P and / or Si in an amount of up to 10% by weight, preferably up to 5 wt .-%, based on titanium dioxide.
  • binders such as Water glass, carboxymethyl celluloses or polyvinyl alcohols and / or plasticizers such as e.g. Polyphosphates or polyacrylates can be added to the TiO2 hydrate in an amount of 0.1 to 5% by weight each before the calcination.
  • a significant advantage of the process is that you can get to the end product directly from a TiO2 pigment precursor, a precipitated TiO2 hydrate, in just one process step using the inexpensive short-term calcination.
  • the calcination of the TiO2 hydrate is carried out in an oxidizing or reducing atmosphere.
  • the reducing procedure has the advantage that, if sulfuric acid-containing TiO2 hydrate is used, more SO2 than SO3 is present in the gaseous fission products formed during the calcination from the sulfate. In the subsequent product separation outside the reaction chamber, SO2 is less adsorbed back to the TiO2 surface than SO3.
  • the titanium dioxide according to the invention can be used as an opacifier in the production of enamels or glazes.
  • a titanium dioxide hydrate suspension with a TiO2 content of 25.5 wt .-%, a sulfate content of 7.5 wt .-%, based on TiO2, and a BET surface area of the titanium dioxide hydrate of 280 m2 / g is in a hot gas atomization reactor under a reducing atmosphere calcined at 1050 ° C within 0.5 seconds.
  • a hot carrier gas is countercurrently directed towards the product stream with swirling, with a high-level and uniform mixing of the introduced material with the hot gases.
  • the product is separated outside the hot gas atomization reactor in a cyclone.
  • the product obtained consists predominantly of isometric primary particles of approximately 0.5 ⁇ m, which are predominantly aggregated to spherulitic particles with an average diameter of 13 ⁇ m.
  • the BET surface area is 3.1 m2 / g, the bulk density 0.5 kg / l, the rutile content 61%, the sulfate content 0.03% by weight, based on TiO2, and the TiO2 content 99.5%. -%.
  • the product does not stick and shows an excellent mixing and digestion behavior in a bortitanium white enamel frit. After application and penetration, a high reflectivity, a high covering power and a favorable color of the enamelling are obtained.
  • a TiO2 hydrate suspension as described in Example 1 is added 1 wt .-% phosphoric acid based on TiO2. It is then calcined at 1080 ° C. for 0.5 seconds under a reducing atmosphere.
  • the product obtained consists predominantly of 0.7 ⁇ m large primary particles, which are mainly aggregated to spherulitic particles with an average diameter of 16 ⁇ m.
  • the BET surface area is 2.8 m2 / g, the bulk density 0.55 kg / l, the rutile content 76%, the sulfate content 0.02% by weight, based on TiO2, and the TiO2 content 99.0%. -%.
  • the product shows an excellent mixing and digestion behavior in the enamel frit. After application and branding, a very high opacity with a bluish hue is obtained in the enamel.

Description

Die vorliegende Erfindung betrifft Titandioxid, ein Verfahren zu seiner Herstellung und seine Verwendung in glasartigen Emails und Schmelzglasuren als Trübungsmittel.The present invention relates to titanium dioxide, a process for its preparation and its use in glass-like enamels and glazes as opacifiers.

Titandioxid wird als Farbpigment entweder durch Umsetzung von TiCl₄ mit O₂ oder durch Hydrolyse einer schwefelsäurehaltigen, wäßrigen Lösung von Titanylsulfat und nachfolgender Kalzinierung hergestellt.Titanium dioxide is produced as a color pigment either by reacting TiCl₄ with O₂ or by hydrolysis of an aqueous solution of titanyl sulfate containing sulfuric acid and subsequent calcination.

Im Falle des Sulfatprozesses wird die Titandioxidhydrat-Suspension in einem Drehrohrofen bei Verweilzeiten von 5 bis 20 Stunden kalziniert. Der bei der Hydrolyse anfallende Niederschlag besteht aus feinen Teilchen mit einer spezifischen BET-Oberfläche von 50-500 m²/g, die eine starke Agglomerierung während der Kalzinierung erfahren.In the case of the sulfate process, the titanium dioxide hydrate suspension is calcined in a rotary tube furnace with residence times of 5 to 20 hours. The precipitate resulting from the hydrolysis consists of fine particles with a specific BET surface area of 50-500 m² / g, which undergo strong agglomeration during the calcination.

Die sich durch Kalzinierung ergebenden Agglomerate bilden Teilchen von 0,1 bis 1,0 mm, die sich aus Primärteilchen von 0,2 bis 0,4 µm zusammensetzen. Dieses Material ist als Klinker oder auch als gemahlenes Pigment zur Einarbeitung in glasartige Emails oder Schmelzglasuren wenig geeignet, da es sich zusammenballt, wenn es in trockenem Zustand mit den übrigen Bestandteilen der Emailfritte gemischt wird, was zu einer unvollständigen und inhomogenen Lösung des Titandioxids während des Schmelzvorganges der Fritte führt.The agglomerates resulting from calcination form particles of 0.1 to 1.0 mm, which are composed of primary particles of 0.2 to 0.4 µm. This material is not very suitable as a clinker or as a ground pigment for incorporation into glass-like enamels or enamels, since it clumps when mixed with the other constituents of the enamel frit in a dry state, which leads to an incomplete and inhomogeneous solution of the titanium dioxide during the The frit melts.

In der deutschen Auslegeschrift 1 207 363 wird ein Verfahren zur Herstellung eines TiO₂-Produktes für die Einarbeitung in glasartigen Emails durch Kalzinierung von gefälltem Titandioxidhydrat beschrieben. Dabei wird ein gefälltes Titandioxidhydrat mit grober Teilchengröße, das aus Primärteilchen von 5 bis 20 µm besteht, mit einem gefällten Titandioxidhydrat feiner Teilchengröße, das aus Primärteilchen von vorwiegend unter 1 µm besteht, wie es bei der Herstellung von TiO₂-Pigmenten anfällt, gemischt, und die Mischung wird kalziniert. Der Nachteil dieses Verfahrens besteht darin, daß es aufgrund der zwei stark unterschiedlichen Titandioxidhydrate, die erst hergestellt werden müssen, sehr aufwendig wird. Weiterhin besteht der Nachteil derartig erhaltenem TiO₂ darin, daß es sich durch ein hohes Schüttgewicht von 1,4 bis 2 kg/l auszeichnet und eine niedrige spezifische Oberfäche von deutlich unter 1 m² /g aufweist, was zu geringer Reaktivität beim Aufschmelzen in der Fritte führt.In German Auslegeschrift 1 207 363 a process for the production of a TiO₂ product for incorporation in glass-like enamels by calcining precipitated titanium dioxide hydrate is described. A precipitated titanium dioxide hydrate with a coarse particle size, which consists of primary particles of 5 to 20 μm, is mixed with a precipitated titanium dioxide hydrate, which consists of primary particles of primarily less than 1 μm, as is produced in the production of TiO 2 pigments, and the mixture is calcined. The disadvantage of this method is that it is very expensive due to the two very different titanium dioxide hydrates that have to be prepared first. Furthermore, the disadvantage of TiO₂ obtained in this way is that it is characterized by a high bulk density of 1.4 to 2 kg / l and has a low specific surface area of well below 1 m² / g, which leads to low reactivity when melting in the frit .

In der US-A 2 721 787 werden freifließende, nichtstaubende Aggregate bestehend aus kalziniertem Anatas (Primärteilchengröße 0,2 bis 0,3 µm, spezifische Oberfläche 4,5 bis 9 m²/g) und 0,1 bis 3 % eines anorganischen Bindemittels beschrieben. Diese Aggregate werden hergestellt, indem wäßrige Slurries aus hydroklassifizierten Titandioxidpigmenten, die aus der normalen Pigmentherstellung stammen, bei 150 bis 400°C sprühgetrocknet werden. Der Nachteil dieses Verfahrens liegt darin, daß zuerst kalzinierte Titandioxidpigmente hergestellt werden müssen, die dann in Wasser zur Herstellung einer Slurry aufgenommen werden, um diese Slurry danach sprühzutrocknen, um die beanspruchten Aggregate zu erhalten.US Pat. No. 2,721,787 describes free-flowing, non-dusting aggregates consisting of calcined anatase (primary particle size 0.2 to 0.3 μm, specific surface area 4.5 to 9 m 2 / g) and 0.1 to 3% of an inorganic binder . These aggregates are produced by spray-drying aqueous slurries of hydro-classified titanium dioxide pigments, which originate from normal pigment production, at 150 to 400 ° C. The disadvantage of this process is that calcined titanium dioxide pigments must first be prepared, which are then taken up in water to produce a slurry, in order to then spray-dry this slurry in order to obtain the claimed aggregates.

In der US-A 3 018 186 wird plättchenförmiges Titandioxid mit einem Durchmesser von 1-20 µm und einer Dicke von 0,01-0,5 µm beschrieben, das fast ausschließlich in der Rutilmodifikation vorliegt. Diese Plättchen werden hergestellt, indem eine Titanylsulfatlösung, die mindestens 5 und höchstens 20 % an Schwefelsäure enthält, in einer Flamme bei 800°C bis 1800°C und Verweilzeiten von 0,001-0,5 Sekunden kalziniert wird. Das erhaltene Material ist frei von Schwefelsäure und wird in keramischen und elektrischen Massen, Kunststoffen und Oberflächenbeschichtungen sowie als Füllstoff eingesetzt. Die eingesetzte Titanylsulfatlösung ist aufwendig herzustellen, da sie in reiner Form kein Zwischenprodukt des Pigmentherstellungsprozesses darstellt. Die durch Aufschluß von Titanerzen anfallende Lösung enthält erhebliche Mengen an Fremdelementen wie Fe, Al, Mg u.a.US Pat. No. 3,018,186 describes platelet-shaped titanium dioxide with a diameter of 1-20 μm and a thickness of 0.01-0.5 μm, which is almost exclusively in the rutile modification. These platelets are produced by calcining a titanyl sulfate solution containing at least 5% and at most 20% sulfuric acid in a flame at 800 ° C to 1800 ° C and residence times of 0.001-0.5 seconds. The material obtained is free of sulfuric acid and is used in ceramic and electrical materials, plastics and surface coatings as well as a filler. The titanyl sulfate solution used is complex to produce, since in pure form it is not an intermediate represents the pigment manufacturing process. The solution obtained by digestion of titanium ores contains considerable amounts of foreign elements such as Fe, Al, Mg and others

Aufgabe war es daher, ein geeignetes Titandioxid, das als Trübungsmitel für glasartige Emails und Schmelzglasuren eingesetzt werden kann, zur Verfügung zu stellen.The task was therefore to provide a suitable titanium dioxide, which can be used as a clouding agent for glassy enamels and enamels.

Es wurde nun gefunden, daß das erfindungsgemäße Titandioxid die obengenannten Anforderungen erfüllt. Dieses Titandioxid weist überwiegend isometrische Primärteilchen der Größe von 0,5 bis 5,0 µm auf, die zu überwiegend sphärolithischen Partikeln mit Durchmessern von 1 bis 100 µm aggregiert sind, und hat eine BET-Oberfläche von 1 bis 4,5 m²/g und ein Schüttgewicht von 0,2 bis 1,3 kg/l. Die BET-Oberfläche wird nach DIN 66 131, Abschnitt 6, Okt. 1973 bestimmt (5-Punkt-Methode, Meßgas: Stickstoff, Adsorption bei der Temperatur des siedenden Stickstoffs, Annahme des Flächenbedarfs eines Stickstoffmoleküls von 0,162 nm², Vorbehandlung: 1 Stunde Ausheizen im Stickstoffstrom bei 130°C).It has now been found that the titanium dioxide according to the invention fulfills the above-mentioned requirements. This titanium dioxide predominantly has isometric primary particles of the size from 0.5 to 5.0 μm, which are aggregated to predominantly spherulitic particles with diameters from 1 to 100 μm, and has a BET surface area of 1 to 4.5 m² / g and a bulk density of 0.2 to 1.3 kg / l. The BET surface area is determined according to DIN 66 131, Section 6, Oct. 1973 (5-point method, measuring gas: nitrogen, adsorption at the temperature of the boiling nitrogen, assumption of the area requirement of a nitrogen molecule of 0.162 nm², pretreatment: 1 hour of heating in a stream of nitrogen at 130 ° C).

Dieses Titandioxid zeigt eine gute Stabilität, d.h., es zerfällt beim Mischen nicht in Feinkorn. Die Härte ist andererseits nicht so groß, so daß sich in Verbindung mit der Primärpartikelgröße von 0,5 bis 5 µm und der spezifischen Oberfläche von 1 bis 4,5 m²/g ein ausgezeichnetes Aufschlußverhalten des Titandioxids in der Emailschmelze ergibt. Die 1 bis 100 µm großen agglomerierten Partikel verteilen sich beim Mischen sehr gleichmäßig in der Fritte und schmelzen anschließend vollständig auf. Besonders günstig ist das Aufschlußverhalten, wenn das erfindungsgemäße Titandioxid ein Schüttgewicht von 0,2 bis 0,8 kg/l aufweist.This titanium dioxide shows good stability, ie it does not break down into fine grains when mixed. On the other hand, the hardness is not so great that, in combination with the primary particle size of 0.5 to 5 µm and the specific surface area of 1 to 4.5 m² / g, the titanium dioxide has excellent digestion behavior Enamel melt results. The 1 to 100 µm agglomerated particles are distributed evenly in the frit when mixed and then melt completely. The digestion behavior is particularly favorable if the titanium dioxide according to the invention has a bulk density of 0.2 to 0.8 kg / l.

In der abgeschreckten Fritte bilden die Partikel titandioxidreiche Nahbezirke, die im Anfangsstadium des Emailbrands als Keimzellen für die Titandioxidrekristallisation wirken.In the quenched frit, the particles form nearby areas rich in titanium dioxide, which act as germ cells for the recrystallization of titanium dioxide in the early stages of enamel firing.

Im weiteren Verlauf des Emailbrands wird dann nahezu ausschließlich Anatas in geeigneter Kristallitgröße, isometrischer Form und gleichmäßiger Verteilung erzeugt, wodurch ein hohes Reflexionsvermögen bei ausgezeichneter Deckkraft erhalten wird.In the further course of the enamel firing, almost exclusively anatase in a suitable crystallite size, isometric shape and even distribution is produced, whereby a high reflectivity with excellent opacity is obtained.

In einer besonderen Ausführungsform liegt das erfindungsgemäße Titandioxid mit über 50 Gew.-% als Rutil vor und weist einen Sulfatgehalt unterhalb 0,5 Gew.-%, vorzugsweise unterhalb 0,3 Gew.-%, gerechnet als Sulfat und auf Titandioxid bezogen, sowie einen Titandioxidgehalt oberhalb 90 Gew.-% auf.In a particular embodiment, the titanium dioxide according to the invention is present as rutile with more than 50% by weight and has a sulfate content below 0.5% by weight, preferably below 0.3% by weight, calculated as sulfate and based on titanium dioxide, and a titanium dioxide content above 90% by weight.

Restwassermengen bis zu 3 Gew.-%, bezogen auf Titandioxid, beeinflußen die Produktqualität nicht.Residual water quantities of up to 3% by weight, based on titanium dioxide, do not influence the product quality.

In einer weiteren Ausführungsform enthält das Titandioxid Oxide, Phosphate und/oder Silikate der Metalle Li, Na und/oder K in einer Menge von bis zu 0,5 Gew.-%, bezogen auf Titandioxid, und/oder Mg, Ca, Sr, Ba, Sn, Sb, Bi, Y, Zr, Zn, V, Nb, W und/oder Mo und/oder Oxide der Elemente P und/oder Si in einer Menge bis zu 10 Gew.-%, vorzugsweise bis zu 5 Gew.-%, bezogen auf Titandioxid. So verbessert beispielsweise ein Zusatz von P₂O₅ die TiO₂-Rekristallisation und somit die Trübung im Email. ein Zusatz von WO₃ den Farbton im Email und ein Zusatz von K₂O in einer Menge von bis zu 0,5 Gew.-%, vorzugsweise von 0,1 bis 0,2 Gew.-%, bezogen auf TiO₂, das Aufschlußverhalten in der Fritte und den Farbton im Email, Überraschenderweise ist hierbei die ursprüngliche, räumliche Entfernung der Zusatzstoffe vom TiO₂-Korn für die nachfolgende TiO₂-Trübung von großer Wichtigkeit, d.h., ein Einbringen derselben Zusatzstoffe in derselben Menge direkt in die Fritte hätte einen weitaus geringeren Effekt zur Folge.In a further embodiment, the titanium dioxide contains oxides, phosphates and / or silicates of the metals Li, Na and / or K in an amount of up to 0.5% by weight, based on titanium dioxide, and / or Mg, Ca, Sr, Ba, Sn, Sb, Bi, Y, Zr, Zn, V, Nb, W and / or Mo and / or oxides of the elements P and / or Si in an amount of up to 10% by weight, preferably up to 5% by weight, based on Titanium dioxide. For example, an addition of P₂O₅ improves the TiO₂ recrystallization and thus the turbidity in the enamel. an addition of WO₃ the color in the enamel and an addition of K₂O in an amount of up to 0.5 wt .-%, preferably 0.1 to 0.2 wt .-%, based on TiO₂, the digestion behavior in the frit and the color in the enamel. Surprisingly, the original spatial removal of the additives from the TiO₂ grain is of great importance for the subsequent TiO₂ cloudiness, ie introducing the same additives in the same amount directly into the frit would have a far less effect .

Gegenstand der Erfindung ist weiterhin ein geeignetes Verfahren zur Herstellung des erfindungsgemäßen Titandioxids, wobei Titandioxidhydrat mit einer BET-Oberfläche von 50 bis 500 m²/g einer Kurzzeitkalzination bei Verweilzeiten von 0,1 bis 60 Sekunden und bei Temperaturen von 800 bis 1600°C ausgesetzt wird.The invention further relates to a suitable process for the preparation of the titanium dioxide according to the invention, wherein titanium dioxide hydrate with a BET surface area of 50 to 500 m² / g is subjected to a short-term calcination with residence times of 0.1 to 60 seconds and at temperatures of 800 to 1600 ° C. .

Überraschend dabei ist, daß diese Kurzzeitkalzination des Titandioxidhydrates bei den obengenannten Temperaturen trotz der geringen Reaktionszeiten ein deutliches Kristallitwachstum zu 0,5 bis 5,0 µm großen, überwiegend isometrischen Primärteilchen sowie eine nahezu vollständige Säureabspaltung bewirkt. Die gesinterten Primärteilchen sind über Sinterbrücken zu 1 bis 100 µm großen Partikeln aggregiert, die als Pigment zur Einfärbung von Farben oder Kunststoffen nicht geeignet sind, jedoch ausgezeichnete Eigenschaften als Trübungsmittel in Emails aufweisen.It is surprising that this short-term calcination of the titanium dioxide hydrate at the above-mentioned temperatures, despite the short reaction times, causes a clear crystallite growth to predominantly isometric primary particles of 0.5 to 5.0 μm in size and an almost complete elimination of acid. The sintered primary particles are aggregated via sintered bridges to 1 to 100 µm large particles, which act as a pigment for coloring Paints or plastics are not suitable, but have excellent properties as opacifiers in enamels.

Das TiO₂-Hydrat kann über eine Ein- bzw. Mehrstoffdüse als wäßrige Suspension in den Kalzinierer eingetragen werden. Es ist jedoch auch möglich, das Ausgangsmaterial in Form einer pastösen Masse bzw. als trockenes Pulver dem Kalzinierer zuzuführen. Als Kurzzeitkalzinierer kommen übliche Apparaturen wie z.B. Heißgaszerstäubungsreaktoren, Reaktionszyklone oder Flash-Kalzinierer in Betracht, die normalerweise mit direkter Heizgaszuführung arbeiten. Eine indirekte Beheizung ist jedoch ebenfalls möglich.The TiO₂ hydrate can be introduced as an aqueous suspension into the calciner via a single or multi-component nozzle. However, it is also possible to feed the starting material to the calciner in the form of a pasty mass or as a dry powder. Short-term calciners come with conventional equipment such as Hot gas atomization reactors, reaction cyclones or flash calciners, which normally work with direct heating gas supply. However, indirect heating is also possible.

Die Produktabscheidung erfolgt außerhalb der Kalzinierkammer beispielsweise über einen Zyklon oder elektrischen bzw. mechanischen Pulverabscheider.The product is separated outside the calcining chamber, for example using a cyclone or electrical or mechanical powder separator.

In einer bevorzugten Ausführungsform wird die Kalzination des TiO₂-Hydrats zwischen 1000 und 1300°C bei Verweilzeiten von 0,1 bis 5 Sekunden durchgeführt.In a preferred embodiment, the calcination of the TiO₂ hydrate is carried out between 1000 and 1300 ° C. with residence times of 0.1 to 5 seconds.

Als Ausgangsmaterial für die Kurzzeitkalzination wird Titandioxidhydrat mit bis zu 30 Gew.-% Sulfat, bezogen auf Titandioxid oder vorzugsweise gefälltes schwefelsäurehaltiges Titandioxidhydrat eingesetzt, wie es z.B. beim Pigmentherstellungsprozeß nach dem Sulfatverfahren anfällt.Titanium dioxide hydrate with up to 30% by weight sulfate, based on titanium dioxide or preferably precipitated sulfuric acid-containing titanium dioxide hydrate, is used as the starting material for the short-term calcination, as is e.g. arises in the pigment production process using the sulfate process.

Dem Titandioxidhydrat können in einer bevorzugten Ausführungsform vor der Kalzination Hilfsstoffe in geeigneter Form untergemischt werden, die nach der Kalzination als Oxide, Phosphate und/oder Silikate der Elemente Li, Na und/oder K in einer Menge von bis zu 0,5 Gew.-%, bezogen auf Titandioxid und/oder Mg, Ca, Sr, Ba, Sn, Sb, Bi, Y, Zi, Zn, V, Nb, W und/oder Mo und/oder als Oxide der Elemente P und/oder Si in einer Menge bis zu 10 Gew.-%, vorzugsweise bis zu 5 Gew.-%, bezogen auf Titandioxid, vorliegen.In a preferred embodiment, auxiliary substances can be added to the titanium dioxide hydrate in a suitable manner before the calcination Form are mixed, which after calcination as oxides, phosphates and / or silicates of the elements Li, Na and / or K in an amount of up to 0.5 wt .-%, based on titanium dioxide and / or Mg, Ca, Sr , Ba, Sn, Sb, Bi, Y, Zi, Zn, V, Nb, W and / or Mo and / or as oxides of the elements P and / or Si in an amount of up to 10% by weight, preferably up to 5 wt .-%, based on titanium dioxide.

Auch Bindemittel wie z.B. Wasserglas, Carboxymethylcellulosen oder Polyvinylalkohole und/oder Verflüssiger wie z.B. Polyphosphate oder Polyacrylate können dem TiO₂-Hydrat vor der Kalzinierung in einer Menge von jeweils 0,1 bis 5 Gew.-% zugemischt werden.Also binders such as Water glass, carboxymethyl celluloses or polyvinyl alcohols and / or plasticizers such as e.g. Polyphosphates or polyacrylates can be added to the TiO₂ hydrate in an amount of 0.1 to 5% by weight each before the calcination.

Ein erheblicher Vorteil des Verfahrens liegt darin, daß man in lediglich einem Verfahrensschritt direkt von einem TiO₂- Pigmentvorprodukt, einem gefällten TiO₂-Hydrat, mit Hilfe der kostengünstigen Kurzzeitkalzination zum Endprodukt gelangt.A significant advantage of the process is that you can get to the end product directly from a TiO₂ pigment precursor, a precipitated TiO₂ hydrate, in just one process step using the inexpensive short-term calcination.

Die Kalzinierung des TiO₂-Hydrats wird in oxidierender oder reduzierender Atmosphäre durchgeführt. Die reduzierende Fahrweise hat den Vorteil, daß im Falle des Einsatzes von schwefelsäurehaltigem TiO₂-Hydrat in den bei der Kalzinierung aus dem Sulfat entstehenden gasförmigen Spaltprodukten mehr SO₂ als SO₃ vorliegt. Bei der anschließenden Produktabscheidung außerhalb der Reaktionskammer wird SO₂ weniger stark an die TiO₂-Oberfläche zurückadsorbiert als SO₃.The calcination of the TiO₂ hydrate is carried out in an oxidizing or reducing atmosphere. The reducing procedure has the advantage that, if sulfuric acid-containing TiO₂ hydrate is used, more SO₂ than SO₃ is present in the gaseous fission products formed during the calcination from the sulfate. In the subsequent product separation outside the reaction chamber, SO₂ is less adsorbed back to the TiO₂ surface than SO₃.

Das erfindungsgemäße Titandioxid kann als Trübungsmittel bei der Herstellung von Emails oder Schmelzglasuren verwendet werden.The titanium dioxide according to the invention can be used as an opacifier in the production of enamels or glazes.

Nachfolgend wird die Erfindung anhand der Beispiele 1 und 2 näher erläutert, ohne daß diese einschränkend wirken.The invention is explained in more detail below with reference to Examples 1 and 2, without these having a restrictive effect.

Beispiel 1example 1

Eine Titandioxidhydratsuspension mit einem TiO₂-Gehalt von 25,5 Gew.-%, einem Sulfatgehalt von 7,5 Gew.-%, bezogen auf TiO₂, und einer BET-Oberfläche des Titandioxidhydrates von 280 m²/g wird in einem Heißgaszerstäubungsreaktor unter reduzierender Atmosphäre innerhalb 0,5 Sekunden bei 1050°C kalziniert. In der Reaktionskammer des Reaktors wird ein heißes Trägergas im Gegenstrom unter Verwirbelung dem Produktstrom entgegengeführt, wobei eine hochgradige und gleichmäßige Durchmischung des eingetragenen Gutes mit den heißen Gasen erfolgt. Die Produktabscheidung erfolgt außerhalb des Heißgaszerstäubungsreaktors in einem Zyklon. Das erhaltene Produkt besteht vorwiegend aus isometrischen Primärteilchen von etwa 0,5 µm, die überwiegend zu sphärolithischen Partikeln mit einem mittleren Durchmesser von 13 µm aggregiert sind. Die BET-Oberfläche beträgt 3,1 m²/g, das Schüttgewicht 0,5 kg/l, der Rutilanteil 61 %, der Sulfatgehalt 0,03 Gew.-%, bezogen auf TiO₂, und der TiO₂-Gehalt 99,5 Gew.-%.A titanium dioxide hydrate suspension with a TiO₂ content of 25.5 wt .-%, a sulfate content of 7.5 wt .-%, based on TiO₂, and a BET surface area of the titanium dioxide hydrate of 280 m² / g is in a hot gas atomization reactor under a reducing atmosphere calcined at 1050 ° C within 0.5 seconds. In the reaction chamber of the reactor, a hot carrier gas is countercurrently directed towards the product stream with swirling, with a high-level and uniform mixing of the introduced material with the hot gases. The product is separated outside the hot gas atomization reactor in a cyclone. The product obtained consists predominantly of isometric primary particles of approximately 0.5 μm, which are predominantly aggregated to spherulitic particles with an average diameter of 13 μm. The BET surface area is 3.1 m² / g, the bulk density 0.5 kg / l, the rutile content 61%, the sulfate content 0.03% by weight, based on TiO₂, and the TiO₂ content 99.5%. -%.

Das Produkt klebt nicht und zeigt ein ausgezeichnetes Misch- und Aufschlußverhalten in einer Bortitanweißemailfritte. Nach Auftrag und Einbrand wird ein hohes Reflexionsvermögen, eine hohe Deckkraft und ein günstiger Farbton der Emaillierung erhalten.The product does not stick and shows an excellent mixing and digestion behavior in a bortitanium white enamel frit. After application and penetration, a high reflectivity, a high covering power and a favorable color of the enamelling are obtained.

Beispiel 2Example 2

Einer TiO₂-Hydratsuspension wie in Beispiel 1 beschrieben wird 1 Gew.-% Phosphorsäure bezogen auf TiO₂ zugesetzt. Anschließend wird unter reduzierender Atmosphäre 0,5 Sekunden bei 1080°C kalziniert. Das erhaltene Produkt besteht vorwiegend aus 0,7 µm großen Primärteilchen, die überwiegend zu sphärolithischen Partikeln mit einem mittleren Durchmesser von 16 µm aggregiert sind. Die BET-Oberfläche beträgt 2,8 m²/g, das Schüttgewicht 0,55 kg/l, der Rutilanteil 76 %, der Sulfatgehalt 0,02 Gew.-%, bezogen auf TiO₂, und der TiO₂-Gehalt 99,0 Gew.-%.A TiO₂ hydrate suspension as described in Example 1 is added 1 wt .-% phosphoric acid based on TiO₂. It is then calcined at 1080 ° C. for 0.5 seconds under a reducing atmosphere. The product obtained consists predominantly of 0.7 μm large primary particles, which are mainly aggregated to spherulitic particles with an average diameter of 16 μm. The BET surface area is 2.8 m² / g, the bulk density 0.55 kg / l, the rutile content 76%, the sulfate content 0.02% by weight, based on TiO₂, and the TiO₂ content 99.0%. -%.

Das Produkt zeigt ein ausgezeichnetes Misch- und Aufschlußverhalten in der Emailfritte. Nach Auftrag und Einbrand wird eine sehr hohe Opazität bei blaustichigem Farbton im Email erhalten.The product shows an excellent mixing and digestion behavior in the enamel frit. After application and branding, a very high opacity with a bluish hue is obtained in the enamel.

Claims (11)

1. Titanium dioxide, characterized in that it contains predominantly isometric primary particles between 0.5 and 5.0 µm in size, which are aggregated into predominantly spherolithic particles between 1 and 100 µm in diameter, and has a BET surface of 1 to 4.5 m²/g and an apparent density of 0.2 to 1.3 kg/l.
2. Titanium dioxide as claimed in claim 1, characterized in that it has an apparent density of 0.2 to 0.8 kg/l.
3. Titanium dioxide as claimed in claim 1 or 2, characterized in that it is more than 50% by weight rutile and has a sulfate content below 0.5% by weight and preferably below 0.3% by weight, expressed as sulfate and based on titanium dioxide, and a TiO₂ content above 90% by weight.
4. Titanium dioxide as claimed in any of claims 1 to 3, characterized in that it contains oxides, phosphates and/or silicates of the metals Li, Na and/or K in a quantity of up to 0.5% by weight, based on titanium dioxide, and/or Mg, Ca, Sr, Ba, Sn, Sb, Bi, Y, Zr, Zn, V, Nb, W and/or Mo and/or oxides of the elements P and/or Si in a quantity of up to 10% by weight and preferably up to 5% by weight, based on titanium dioxide.
5. A process for the production of the titanium dioxide claimed in claim 1 or 2, characterized in that titanium dioxide hydrate having a BET surface of 50 to 500 m²/g is subjected to short-time calcination for 0.1 to 60 seconds at temperatures of 800 to 1,600°C.
6. A process for the production of the titanium dioxide claimed in claim 3, characterized in that titanium dioxide hydrate having a BET surface of 50 to 500 m²/g, which contains up to 30% by weight sulfate - based on titanium dioxide - before calcination, is subjected to short-time calcination for 0.1 to 60 seconds at temperatures of 800 to 1,600°C.
7. A process for the production of the titanium dioxide claimed in claim 4, characterized in that titanium dioxide hydrate having a BET surface of 50 to 500 m²/g which, before calcination, contains oxides, phosphates and/or silicates of the metals Li, Na and/or K in a quantity of up to 0.5% by weight, based on titanium dioxide, and/or Mg, Ca, Sr, Ba, Sn, Sb, Bi, Y, Zr, Zn, V, Nb, W and/or Mo and/or oxides of the elements P and/or Si in a quantity of up to 10% by weight and preferably up to 5% by weight, based on titanium dioxide, and/or compounds which, after calcination, give oxides, phosphates and/or silicates of the said elements in the corresponding quantities is subjected to short-time calcination for 0.1 to 60 seconds at temperatures of 800 to 1,600°C.
8. A process as claimed in claims 5 to 7, characterized in the the TiO₂ hydrate is calcined for 0.1 to 5 seconds at 1,000 to 1,300°C.
9. A process as claimed in claims 5 to 8, characterized in that TiO₂ hydrate containing sulfuric acid is used.
10. A process as claimed in claims 5 to 9, characterized in that the TiO₂ hydrate is calcined in an oxidizing or reducing atmosphere.
11. The use of the titanium dioxide as claimed in one or more of claims 1 to 4 as an opacifier in the production of enamels or enamel glazes.
EP89121252A 1988-11-29 1989-11-17 Titanium dioxide, process for its preparation and use thereof Expired - Lifetime EP0371343B1 (en)

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